Aerospace medicine

(medicine) The branch of medicine dealing with the effects of flight in the atmosphere or space upon the human body and with the prevention or cure of physiological or psychological malfunctions arising from these effects. Also known as aeromedicine; aviation medicine.

The special field of medicine that deals with humans in environments encountered beyond the surface of the Earth. It includes both aviation medicine and space medicine and is concerned with humans, their environment, and the vehicles in which they fly. Its objective is to ensure human health, safety, well-being, and effective performance through careful selection and training of flight personnel, protection from the unique flight environment and its physiological and psychological effects, and understanding of the flight vehicle and humans' interaction with it.

The environment encountered in air or space flight is very different from that on Earth. Consequently aerospace medicine must deal with the physics of the atmosphere and space and with the conditions and influences introduced by the flight vehicle. Aerospace medicine is therefore concerned with the physiological effects of changes in barometric pressure, atmospheric constituents, toxic substances, acceleration, weightlessness, noise, vibration, ionizing radiation, and thermal and other environmental stresses, as well as psychological stresses and their effects on behavior and performance.

The flight conditions of advanced supersonic aircraft introduce extreme variations in temperature, extensive and sudden changes in pressure, and rapid acceleration. Exposure to the low pressure at altitudes may release nitrogen gas normally held in the blood in solution and thus produce bends symptoms. As altitude increases, oxygen continues to constitute 21% of the atmosphere, but the decreased pressure of the upper atmosphere and consequently of the oxygen results in reduced oxygenation of the blood, affecting physical well-being and the ability to think and to reason. The physiological problems of acceleration are an integral part of aerospace medicine because humans are exposed to forces of acceleration almost constantly throughout flight that are different from the 1-g environment of Earth. When positive g (increased acceleration) forces are applied to the body, the blood is forced downward away from the head and heart, and blackout and unconsciousness may occur. Under negative g (decreased acceleration) conditions, the blood is forced upward so that the blood vessels of the head are engorged. This may result in redout, a condition in which the visual field reddens due to engorged eye blood vessels, and unconsciousness. See also Acceleration.

All of the environmental hazards incumbent in flight in aircraft are present in space flight, but space also has unique hazards, of which weightlessness is paramount. The equilibrium of many biological systems is disrupted by extended exposure to weightlessness.

Neurovestibular effects associated with space motion sickness occur during the first few days in orbit. At the same time there is a shift in body fluids toward the head, and faces become puffy. This is followed by a loss of fluids and electrolytes. With decreased fluids, red blood cell mass slowly decreases for about 60 days into flight. Cardiovascular deconditioning also occurs within the first month. These systems in general appear to acclimate to the weightless environment in 4–6 weeks. Postflight symptoms include orthostatic intolerance associated with shifts in body fluid and resultant cardiopulmonary neuroreceptor reflex responses. Difficulties in postural equilibrium and occasionally motion sickness accompany neurovestibular readaptation. See also Weightlessness.

The potential biological effects of galactic cosmic radiation include damage to bone marrow and lymphopoietic, intestinal, and gonadal tissues, as well as infertility, cancer induction, and heritable effects. Shielding and radioprotective chemicals afford some protection from space radiation. Total shielding is impossible, however, because of the excess weight it would impart to the spacecraft and the ability of heavy ions to penetrate even heavy shielding. Space medicine consequently has the responsibility to identify appropriate protective procedures, define exposure limits, and develop therapeutic measures. See also Radiation biology.

Countermeasures used to prevent or control deleterious physiological responses to space flight include physical, psychological, pharmacological, and nutritional means. Specifically, these include exercise, especially of the lower extremities, by using unique bicycles and treadmills; a vacuum suit that applies negative pressure to the lower body to stress the cardiovascular system; salt water loading on the last day of flight to increase blood volume and prevent orthostatic intolerance; and nutritional supplements including calcium. Pharmacologic agents may be used to curb space sickness symptoms and to protect against radiation.